The present disclosure relates to a light deflector used in forming an electrostatic latent image and the like, and an optical scanning device and an image forming apparatus with such a light deflector.
In an electrophotographic image forming apparatus, a light beam modulated in accordance with image data is generated, reflected and deflected, whereby an image bearing member such as a photoconductive drum is scanned with the deflected light beam to form an electrostatic latent image. The light deflector is a device for reflecting and deflecting a light beam. A technique using a MEMS (Micro Electro Mechanical Systems) mirror as a light deflector instead of a polygon mirror has been proposed. The MEMS mirror has an advantage of speeded-up scanning, low power consumption and the like.
The light deflector using the MEMS mirror includes a torsion bar, a mirror portion swingable about an axis of the torsion bar and mirror drivers. The mirror portion and the torsion bar are resonated by the mirror drivers and a light beam incident on the mirror portion is scanned by being reflected and deflected in this state.
When the mirror portion is swung about the axis of the torsion bar, an acting moment of inertia is larger on opposite ends of the mirror portion than in a center of the mirror portion in a direction intersecting with the torsion bar. Thus, the mirror portion may be bended when being swung. A light deflector provided with ribs has been proposed to suppress this bend.
This light deflector is provided with a vibrating system composed of a plate-like movable portion, a reflection film formed on the movable portion to reflect light, a first shaft member for supporting the movable portion swingably about an X-axis relative to a supporting member and ribs arranged on the movable portion, and a driving system for swinging the movable portion relative to the supporting member. The ribs are so arranged on one and the other surfaces of the movable portion that a moment of inertia on the one surface and that on the other surface are equal with respect to the first shaft member.
In this light deflector, the ribs are respectively arranged on the one and the other surfaces of the movable portion so that the moment of inertia on the one surface of the movable portion and that on the other surface are equal with respect to the first shaft member (torsion bar). This suppresses movements (e.g. vertical movements) of the movable portion formed with the reflection film other than swinging movements about the first shaft member when the movable portion (mirror portion) formed with the reflection film is swung.